Can't adjust thresholds on float images

[btbest]

Reproduce by adding float probabilities to e.g. oc-from-probabilities and then trying to adjust display threshold on the viewer's probabilities layer. Probably another case of the newer qt version being strict on integers in more widgets.

Affected version: In 1.4.1post1, the thresholding simply doesn't work (it display ranges from 0 to 0). In the current dev environment, ilastik crashes with an error when trying to open the thresholding dialog:

Traceback (most recent call last):
  File "\volumina\volumina\widgets\layercontextmenu.py", line 53, in adjust_thresholds_callback
    dlg = GrayscaleLayerDialog(layer, menu.parent())
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "\volumina\volumina\widgets\layerDialog.py", line 79, in __init__
    self.initialize_range_widgets(
  File "\volumina\volumina\widgets\layerDialog.py", line 56, in initialize_range_widgets
    thresholding_widget.setRange(normalization_range[0], normalization_range[1])
  File "\volumina\volumina\widgets\thresholdingWidget.py", line 69, in setRange
    self._minSlider.setRange(minimum, maximum)
TypeError: setRange(self, min: int, max: int): argument 1 has unexpected type 'numpy.float32'